Metcalf, W. V. (1940). The Reality of the Unobservable. Philosophy of Science. 7 (3): 337—341. doi:10.1086/286640. JSTOR184849.
hkbu.edu.hk
Stephen Palmquist, "The Radical Unknowability of Kant's 'Thing in Itself'", Cogito 3:2 (March 1985), ст.101-115; передруковано як Додаток V Kant's System of Perspectives (University Press of America, 1993).
jstor.org
Metcalf, W. V. (1940). The Reality of the Unobservable. Philosophy of Science. 7 (3): 337—341. doi:10.1086/286640. JSTOR184849.